1. Field of the Invention
The present invention relates to a percussion mechanism having an electrodynamic linear drive.
2. Description of the Related Art
Drilling and/or striking hammers (designated “hammers” hereinafter) are standardly driven by electric motors in which a rotor rotates a drive shaft. The rotational movement is converted into an oscillating linear movement that is communicated to a drive element in a percussion mechanism. Here, as a percussion mechanism in particular a pneumatic spring mechanism is suitable in which a drive piston that acts as a drive element is moved back and forth.
From DE 102 04 861 A1, a pneumatic spring percussion mechanism is known for a hammer in which a drive piston is capable of being driven by an electrodynamic linear drive. The drive piston is coupled to a runner of the linear drive, so that the linear back-and-forth movement of the runner is transmitted to the drive piston. The movement of the drive piston is in turn transmitted (as is standard in pneumatic spring percussion mechanisms) via an air spring to a percussion piston that strikes the end of a tool or strikes an intermediately situated header in a known manner.
In a linear electromagnetic drive system of this sort, the runner and the drive piston coupled thereto must be braked when they reach their extreme positions in order to enable a change in the direction of movement. Only in this way is an oscillating percussive operation possible. During the braking, it, is possible to feed part of the kinetic energy back into an intermediate circuit as electrical energy. However, in the coils of the stator that surrounds the runner, heat loss occurs that has an adverse effect on the efficiency of the percussion system. In addition, the lost heat must be conducted away using a suitable cooling device.
It is therefore advantageous to intermediately store the kinetic energy of the drive unit made up of the runner and the drive piston in a spring, so that after the reversal of the direction of movement this energy is available for the counter-movement, and supports the electromagnetic drive force of the linear drive.
From each of EP 0 718 075 A1 and DE 24 19 164 A1, an electrodynamic drive is known for a percussion mechanism in which a return movement of a percussion piston is received by a mechanical helical spring acting as an end stop. When the percussion piston moves forward again, the helical spring releases the stored energy and thus supports the forward or percussive movement. The described percussion mechanisms are however not pneumatic spring percussion mechanisms, and do not have any separation between a drive piston and a percussion piston.
In addition, helical springs have the disadvantage that they can break due to the high impact speeds. Also, significant vibration noise results. Moreover, if the helical spring is too weak, given a correspondingly high impact speed of the percussion piston the spring can bottom out, which can result in damage to the percussion mechanism.
DE 27 28 485 A1 indicates an electromagnetically operated percussion device in which a shaped piece that acts as a percussion tool is surrounded by a plunger that can be moved cyclically in the impact direction by an electromagnet. At the rear end of the percussion tool, a piston is provided that operates against a pneumatic damper.
From U.S. Pat. No. 1,467,677, an electric hammer is known in which a piston is actuated in alternating fashion by two electromagnets and is moved back and forth in this way. At one end of the piston there is situated a hardened steel tip that strikes a percussion tool. On the opposite side of the piston, an air spring is provided whose strength can be adjusted by opening and closing air ducts.